Propeller for aircraft



April 8, 1941.

F. w. CALDWELL 2.237.924 PROPELLE'R FOR AIRCRAFT Original Filed April21, 1951 IN VEN TOR.

ATTORNEY ntented Apr. 8, 1941 N l T D STATES 110?? 2,237,924: PROPELLER.roe aracasrr Frank W. Caldwell, Hartford, borin assignor to UnitedAircraft Corporation, East Hartford, Conn, a corporation of Delaware(or. vo ic2) 3 Claims.

This invention relates generally to propellers for aircraft and moreparticularly to controllable pitch propellers for aircraft.

An object of the invention is to provide a propeller for aircraft havingblades, the pitch of which may be controlled during flight of theaircraft.

it. further object is to provide improved methods of making andassembling controllable pitch propeller mechanisms.

This application is a division of application Ser. No. 531,685 filedApril 21, 1931, which has now matured into Patent No. 2,032,254 and isalso a division of application Ser. No. 655,144 filed Februaryl2l, 1936,which has now matured into Patent No. 2,138,370. in the accompanyingdrawing, the figure is a longitudinal section of the propeller taken ona plane at right angles to the plane of rotation thereof with portionsof the mechanism shown in full.

Referring to the drawing, a controllable pitch propeller embodying myinvention comprises, in general, a hub structure I mounted a pluralityofpropeller blades 2,, extending from the huh I in the plane of rotationand with their axes in alignment. The hub l is carried, in the usualmanner, on the end of a hollow engine shaft 3. The end of the shaft itis tapered to fit a complementary tapered bore in the hub l, and theexterior of the shaft is splined to mate with a similarly splinedinterior surface of the hub.

The hub is a one-piece structure comprising in general a substantiallycylindrical body portion from which extend integrally formed arms toconstitute a spider having studs on which the blades 2 are mounted. Theparticular blades f shown in the drawing are similar to conventionalmetallic blades insofar as their general shape and aerodynamic qualitiesare, concerned.

The roots or shanlrs of the blades are hollow, and each blade root isbored and fitted with an internal sleeve it having internal bearingsurfaces if and it that engage complementary journals on the arms t. Thebearing surfaces on the arms function to transmit driving torque to theblades and permit them to be turned about their longitudinal axes foradjusting the pitch. The sleeve l l is provided with an integrallaterally extending flange 14 that abuts against the end of the blade 2and is provided with a laterally disposed bearing surface It: thatengages a complementary annular plane bearing surface it on the bodyportion of the hub l enupon which is I circling each stud t to cooperatewith the stud in rigidly holding the blade f.

The end of the blade adjacent the flange it is provided with an integraloutwardly turned flange it to which the flange it is secured by dowelsor screws it. For holding the blades 2 on the studs t with the flangesit tightly against the bearing surfaces it, each blade is provided withan anti-friction thrust bearing it disposed to encircle the blade shankand to bear against the outwardly turned flange ill. The bearings M onthe two blades are inter-connected by a thrust resisting structure orbarrel it, having, at its ends, inwardly turned flanges it that engagethe outer races of the thrust bearings.

As shown, the barrel ft is split along its longitudinal axis in suchmanner that it may be fitted over the blade roots and thesemi-cylindrical halves secured together by suitable bolts (not shown).Openings are provided in substantially the middle of each barrel half topermit it to fit over the cylindrical body portion of the hub i. Thebarrel 24 is made to fit the bearings it closely so that the blades 2are held rigidly in position but may be turned about their longitudinalaxes upon application of relatively large twisting force.

As a method of manufacture, in the event that the blades are of thehollow steel type or of a type in which the flange fl is formed firstand the blade shaped afterwards, the hearing it may be applied to theheated blade after the flange it has been formed, but just before theblade has been pressed to its final shape.

After the hearing it has been applied to the blade shank, the sleeve it,which is preferably of steel, may be inserted. As shown, the enterior ofthe sleeve ii is tapered to fit a complementary tapered surface on theinterior of the blade shank. dleeve ii is made to flt accurately withinthe blade shank and is placed in position by first moderately heatingthe blade, as for instance by dipping the shanlr in hot oil, after whichthe sleeve ii is pressed into the hollow root of the blade to bring itsflange it into contact with the flange ii of its blade root. The bearingsurfaces may be lubricated by graphite or similar material which may beplaced in an annular chamber it adjacent to the annular bearing surfacesit. The action of centrifugal force will force the lubricant outwardlyto lubricate the bearing surfaces if and it.

As shown, the outer end of the sleeve if is reduced to what is known asa feather edge to permit it to flex with the blade during flight andthus avoid concentration of stress in the blade at the end of thesleeve. It is highly important in propeller construction to avoid alllocalization of stress. Fatigue cracks usually start from thatcondition.

By fitting the blades 2 in this manner very accurately and tightly onthe studs 6 of the hub I, wear between the blades and the hub is reducedto a minimum. During flight there is constant vibration in the propellerstructure, particularly in the blades, and if looseness occurs betweenthe blades and the hub, relative motion will result in destructiveabrasion. I

Although the blades 2 are fitted closely to the hub I, it is possible bymeans of suitable apparatus, such as is completely described in theoriginal parent application, Serial No. 531,685, filed April 21, 1931,to turn the blades 2 for adjusting the pitch angle thereof, by means ofan operating lug 3| formed integral with the flange H of the sleeve I Iand extending through a slot 32 in the barrel 24. The slot 32 is made ofsuch length that the blade may be turned through a predetermined maximumangle of adjustment,

but is prevented from turning to a position beyond the predeterminedrange. In a particular practical embodiment of my invention, a torque ofsubstantially 2000 lb. inches is required tomove the two blades 2relative to the spider.

The particular structure shown and the descriptions thereof are for thepurpose only of disclosing complete and workable apparatus and it willbe obvious to others skilled in the art that various modifications inthe details may be made without departing from the scope of theinvention defined in the appended claims.

I claim:

1. A controllable pitch propeller comprising a hub having pivot arms andannular plane bearing surfaces, blades having shanks journalled on thepivot arms, the blades having sleeves in their shanks provided withbearing surfaces for engaging the arms, and said sleeves havingshoulders extending radially at the inner ends of the blades andengaging the annular bearing surfaces on the hub, blade retaining meansfor holding said blades against a tendency to move radially outward dueto the centrifugal force developed in the blades, said pivot arms andsaid sleeve constructed and arranged so that substantially none of thecentrifugal force developed by the blade can be transmitted through thesleeve to the pivot arms.

A controllable pitch propeller comprising a hub having radiallyprojecting pivot arms, each arm having two external cylindrical bearingsurfaces and being encircled by an annular bearing surface on the hubdisposed in a plane transverse to the arm, propeller blades havingsleeves with flanges journalled on the arms, said sleeves engaging thebearing surfaces on the arms and the flanges thereof adapted to engagethe said annular bearing surfaces, blade retaining means acting againstexterior surfaces of the blade for holding said blade against a tendencyto move radially outward due to the centrifugal force developed in theblades, said pivot arms and said sleeves constructed and arranged so asto render said blade and sleeve removable as a unit from said hub.

3. A controllable pitch propeller comprising a hub having pivot arms andannular bearing surfaces encircling said arms, blades having sleeves intheir shanks provided with bearing surfaces for engaging the arms tojournal the blades thereon and having shoulders extending radially atthe inner ends of the blades and engaging the annular bearing surfaceson the hub and means acting on the blades, exterior of the bladesurface, to resist a tendency of the blades to move radially outwardsdue to the efiects of centrifugal force on the blades and to bias saidblade ends toward said shoulders to hold said shoulders against saidannular bearing surfaces.

FRANK W. CALDWELL.

